Leaf nodule endosymbiotic Burkholderia confer targeted allelopathy to their Psychotria hosts.

After a century of investigations, the function of the obligate betaproteobacterial endosymbionts accommodated in leaf nodules of tropical Rubiaceae remained enigmatic. We report that the α-D-glucose analogue (+)-streptol, systemically supplied by mature Ca. Burkholderia kirkii nodules to their Psychotria hosts, exhibits potent and selective root growth inhibiting activity. We provide compelling evidence that (+)-streptol specifically affects meristematic root cells transitioning to anisotropic elongation by disrupting cell wall organization in a mechanism of action that is distinct from canonical cellulose biosynthesis inhibitors. We observed no inhibitory or cytotoxic effects on organisms other than seed plants, further suggesting (+)-streptol as a bona fide allelochemical. We propose that the suppression of growth of plant competitors is a major driver of the formation and maintenance of the Psychotria-Burkholderia association. In addition to potential agricultural applications as a herbicidal agent, (+)-streptol might also prove useful to dissect plant cell and organ growth processes.

Assessment of allelopathic activity of Tradescantia spathacea Sw. for weed control.

Tradescantia spathacea Sw. (Commelinaceae) is widely cultivated as an ornamental and medicinal plant in Southeast Asia, and its pharmacological properties are well known. On the other hand, this plant species is classified as an invasive weed in some countries. As a noxious weed, T. spathacea has been reported to disrupt the growth of native plants. However, no study has reported on its allelopathic activity. Thus, we investigated the allelopathic property and inhibitory substance of T. spathacea. The extracts of T. spathacea significantly inhibited the shoots and roots of alfalfa (Medicago sativa L.), cress (Lepidium sativum L.), lettuce (Lactuca sativa L.), barnyard grass (Echinochloa crus-galli (L.) P. Beauv.), Italian ryegrass (Lolium multiflorum Lam.), and timothy (Phleum pratense L.) at concentrations ≥ 3 mg dry weight (D.W.) equivalent extract/mL. As the extract concentration increased, the growth of the shoots and roots decreased. The I50 values of the test plant shoots and roots were 11.6-72.4 and 5.4-19.5 mg D.W. equivalent extract/mL, respectively. The extracts were purified by column chromatography, and an inhibitory substance was separated, which inhibited the shoots and roots of cress to 18.8 and 11.6% of control growth, respectively. The results of present findings indicate that T. spathacea extracts possess an allelopathic property, and its inhibitory substance may contribute this activity.

Allelopathic effect of Artemisia argyi on the germination and growth of various weeds.

Allelopathy means that one plant produces chemical substances to affect the growth and development of other plants. Usually, allelochemicals can stimulate or inhibit the germination and growth of plants, which have been considered as potential strategy for drug development of environmentally friendly biological herbicides. Obviously, the discovery of plant materials with extensive sources, low cost and markedly allelopathic effect will have far-reaching ecological impacts as the biological herbicide. At present, a large number of researches have already reported that certain plant-derived allelochemicals can inhibit weed growth. In this study, the allelopathic effect of Artemisia argyi was investigated via a series of laboratory experiments and field trial. Firstly, water-soluble extracts exhibited the strongest allelopathic inhibitory effects on various plants under incubator conditions, after the different extracts authenticated by UPLC-Q-TOF-MS. Then, the allelopathic effect of the A. argyi was systematacially evaluated on the seed germination and growth of Brassica pekinensis, Lactuca sativa, Oryza sativa, Portulaca oleracea, Oxalis corniculata and Setaria viridis in pot experiments, it suggested that the A. argyi could inhibit both dicotyledons and monocotyledons not only by seed germination but also by seedling growth. Furthermore, field trial showed that the A. argyi significantly inhibited the growth of weeds in Chrysanthemum morifolium field with no adverse effect on the growth of C. morifolium. At last, RNA-Seq analysis and key gene detection analysis indicated that A.argyi inhibited the germination and growth of weed via multi-targets and multi-paths while the inhibiting of chlorophyll synthesis of target plants was one of the key mechanisms. In summary, the A. argyi was confirmed as a potential raw material for the development of preventive herbicides against various weeds in this research. Importantly, this discovery maybe provide scientific evidence for the research and development of environmentally friendly herbicides in the future.

A study of the phytotoxic effects of the aerial parts of Senecio westermanii Dusén (Asteraceae) on Lactuca sativa L. and Allium cepa L. seeds

The objective of this study was to evaluate the effects of the ethanolic crude extracts and fractions of the species Senecio westermanii Dusén on Lactuca sativa L. (lettuce) and Allium cepa L. (onion) seeds. We assessed the germination, growth, root respiration and photosynthesis of the target species in Petri dishes (9.0 cm diameter) containing filter paper n°6. The study was conducted using 50 seeds per plate and held in 4 replicates per concentration of each sample. In the germination there was an inhibitory effect of fractions hexane (FH) and chloroform (FCl) at concentrations of 500 and 1000 µg/mL. There was a reduction in the radicle growth of lettuce by 14 to 24% and a reduction of hypocotilum by 14 to 28%. As for the radicle of the onion was up 74% reduction to the FCl and the coleoptile was 24 and 45% reduction for FH and FCl, respectively. Inhibitory effects in the root respiration of lettuce were detected in all the samples analyzed, with results ranging from 16 to 83%. For the seeds of A. cepa, there was an encouragement for the FCl and ethyl acetate fractions (FAE), with results ranging from 94 to 142% and 76 to 150%, respectively. With regard to the photosynthesis of L. sativa, there was no significant difference between the control, and as for the A. cepa, there was a strain in inhibition concentrations of 250 and 500 µg/mL, which ranged from 27 to 68%. The samples of S. westermanii caused changes in the target species and thus can be used as a natural herbicide.

N deposition affects allelopathic potential of Amaranthus retroflexus with different distribution regions.

This study aims to determine the allelopathic potential of Amaranthus retroflexus (Ar) with different climatic zones on seed germination and growth of A. tricolor (At) treated with a gradient N addition. Ar leaf extracts only displayed significantly allelopathic potential on the underground growth of Ar but not the aboveground growth of At. The allelopathic potential of Ar leaf extracts on root length of At were enhanced under N addition and there may be a N-concentration-dependent relationship. The effects of the extracts of Ar leaves that collected from Zhenjiang on seed germination and growth of At may be higher than that collected from Jinan especially on root length of At under medium N addition. This reason may be the contained higher concentration of secondary metabolites for the leaves of plants that growths in high latitudes compare with that growth in low latitudes. This phenomenon may also partly be attributed to the fact that Ar originated in America and/or south-eastern Asia which have higher similarity climate conditions as Zhenjiang rather than Jinan. The allelopathic potential of Ar on seed germination and growth of acceptor species may play an important role in its successful invasion especially in the distribution region with low latitudes.

N deposition affects allelopathic potential of Amaranthus retroflexus with different distribution regions

ABSTRACT This study aims to determine the allelopathic potential of Amaranthus retroflexus (Ar) with different climatic zones on seed germination and growth of A. tricolor (At) treated with a gradient N addition. Ar leaf extracts only displayed significantly allelopathic potential on the underground growth of Ar but not the aboveground growth of At. The allelopathic potential of Ar leaf extracts on root length of At were enhanced under N addition and there may be a N-concentration-dependent relationship. The effects of the extracts of Ar leaves that collected from Zhenjiang on seed germination and growth of At may be higher than that collected from Jinan especially on root length of At under medium N addition. This reason may be the contained higher concentration of secondary metabolites for the leaves of plants that growths in high latitudes compare with that growth in low latitudes. This phenomenon may also partly be attributed to the fact that Ar originated in America and/or south-eastern Asia which have higher similarity climate conditions as Zhenjiang rather than Jinan. The allelopathic potential of Ar on seed germination and growth of acceptor species may play an important role in its successful invasion especially in the distribution region with low latitudes.

Seasonal changes in phosphorus competition and allelopathy of a benthic microbial assembly facilitate prevention of cyanobacterial blooms.

Interactions among microbes determine the prevalence of harmful algal blooms that threaten water quality. These interactions can be indirectly mediated by shared resources or consumers, or through interference by the production of allelochemicals. Allelopathic interactions and resource competition have been shown to occur among algae and associated microbes. However, little work has considered seasonal influences on ecosystem structure and function. Here, we report results of our investigations on seasonal changes in the interactions between benthic microbial assemblies and the bloom forming cyanobacterium Microcystis aeruginosa. We show that phosphorus (P) competition and allelopathy by the microbial assembly vary seasonally and inhibit growth of M. aeruginosa. The interactions per unit biomass of the microbial assembly are stronger under winter than summer conditions and inhibit the recruitment of the cyanobacteria, thereby preventing the reoccurrence of cyanobacterial blooms in the following summer. The seasonality of these interactions correlates with changes in composition, metabolic activity and functional diversity of the microbial assembly. Our findings highlight the importance of competitive and allelopathic interactions in regulating the occurrence of harmful algal blooms. Our results also imply that seasonal variation of competition and allelopathy of the microbial assembly might be beneficial to adjust aquatic ecosystem structure and function.

Changes in gametophyte physiology of Pteris multifida induced by the leaf leachate treatment of the invasive Bidens pilosa.

In recent years, the response of fern gametophytes to environment has raised much attention. However, studies on the influence of plant invasion to fern gametophytes are scarce. Allelopathy plays an important role in biological invasion. Hence, it is necessary to study the allelopathic effects of invasive plants on fern gametophytes and elucidate the mechanisms by which invasive plants cause phytotoxicity. As one of the main invasive plants in China, Bidens pilosa exhibits allelopathic effects on spermatophyte growth. Field investigation shows that many ferns are threatened by the invasion of B. pilosa. The distribution of Pteris multifida overlaps with that of B. pilosa in China. To examine the potential involvement of allelopathic mechanisms of B. pilosa leaves, changes in the physiology in P. multifida gametophytes are analyzed. We found that cell membrane and antioxidant enzyme activities as well as photosynthesis pigment contents of the gametophytes were affected by B. pilosa leachates. Gametophytes of P. multifida exposed to B. pilosa had increased damages to cell membranes, expressed in thiobarbituric acid reacting substance (TBARS) concentrations, malondialdehyde (MDA), electrolyte leakage (membrane permeability), and degree of injury. Enzyme activities, assessed by superoxide dismutase (SOD) and catalase (CAT) as well as guaiacol peroxidase (GPX) enhanced with the increase in leachate concentration after 2-day exposure. Meanwhile, lower chlorophyll a (Chl a), chlorophyll b (Chl b), carotenoid (Car), and the total chlorophyll were measured as leachate concentrations increased. At day 10, leaf leachates of B. pilosa exhibited the greatest inhibition. These results suggest that the observed inhibitory or stimulatory effects on the physiology studied can have an adverse effect on P. multifida and that allelopathic interference seems to have involved in this process.

Salvia officinalis L. coverage on plants development / Cobertura de Salvia officinalis L. no desenvolvimento de plantas

ABSTRACT Medicinal plants with essential oils in their composition havetypicallybeen shown to be promising in plant control. Sage (Salvia officinalis L.) is cited for its allelopathic effects. This study evaluated the allelopathic potential of dried sage leaves in vegetation, soil and the development of Lycopersicon esculentum Mill. (tomato), Panicum maximum Jacq. (guinea grass) and Salvia hispanica L. (chia) plants. Three seedlings were transplanted seven days after germination in 1 kg plastic containers with soil, in a greenhouse. The grinded dry mass of sage was placed at rates of 3.75; 7.5 15 t ha-1, and a control (no mass). After 30 days, the chlorophyll index of tomato and guinea grass plants were inhibited with 7.5 and 15 t ha-1 sage cover crops. Tomato shoot length was inhibited in all tested rates, and guinea grass plants showed some reduction in growth when using the highest rate of sage mass (15 t ha-1). The dry mass of tomato and guinea grass plants was reduced when using the15 t ha-1, and 7.5 and 15 t ha-1 of sage cover crops, respectively. It can be concluded that there was some effect of sage coverage on the soil in tomato and guinea grass, but no effect was observed on chia plants.

RESUMO As plantas medicinais que apresentam óleos essenciais em sua composição normalmente têm se mostrado promissoras no controle de plantas. A sálvia (Salvia officinalis L.) é citada por seus efeitos alelopáticos. Assim, esse estudo avaliou o potencial alelopático das folhas secas de sálvia na cobertura vegetal, no solo, sobre o desenvolvimento das plantas de Lycopersicon esculentum Mill. (tomate), Panicum maximum Jacq. (capim mombaça) e Salvia hispanica L. (chia). Três plântulas foram transplantadas, sete dias após germinação, em vasos plásticos de 1 kg, com terra, em casa de vegetação. Sobre elas foi disposta a massa seca triturada de sálvia nas proporções 3,75; 7,5 e 15 t ha-1, além da testemunha (sem massa). Após 30 dias, o teor de clorofila das plantas de tomate e capim mombaça foi inibido com 7,5 e 15 t ha-1 de sálvia em cobertura. O comprimento da parte aérea do tomate foi inibido em todas as proporções testadas e as plantas de capim mombaça apresentaram redução do crescimento quando se utilizou 15 t ha-1 de sálvia como cobertura. A massa seca das plantas de tomate e capim mombaça reduziu com o uso de 15 t ha-1 e, 7,5 e 15 t ha-1 de sálvia como cobertura, respectivamente. Finalmente, pode-se concluir que houve efeito da sálvia em cobertura sobre o solo em tomate e capim mombaça, mas não houve efeito da mesma sobre as plantas de chia.

Identification and Phytotoxicity Assessment of Phenolic Compounds in Chrysanthemoides monilifera subsp. monilifera (Boneseed).

Chrysanthemoides monilifera subsp. monilifera (boneseed), a weed of national significance in Australia, threatens indigenous species and crop production through allelopathy. We aimed to identify phenolic compounds produced by boneseed and to assess their phytotoxicity on native species. Phenolic compounds in water and methanol extracts, and in decomposed litter-mediated soil leachate were identified using HPLC, and phytotoxicity of identified phenolics was assessed (repeatedly) through a standard germination bioassay on native Isotoma axillaris. The impact of boneseed litter on native Xerochrysum bracteatum was evaluated using field soil in a greenhouse. Collectively, we found the highest quantity of phenolic compounds in boneseed litter followed by leaf, root and stem. Quantity varied with extraction media. The rank of phenolics concentration in boneseed was in the order of ferulic acid > phloridzin > catechin > p-coumaric acid and they inhibited germination of I. axillaris with the rank of ferulic acid > catechin > phloridzin > p-coumaric acid. Synergistic effects were more severe compared to individual phenolics. The litter-mediated soil leachate (collected after15 days) exhibited strong phytotoxicity to I. axillaris despite the level of phenolic compounds in the decomposed leachate being decreased significantly compared with their initial level. This suggests the presence of other unidentified allelochemicals that individually or synergistically contributed to the phytotoxicity. Further, the dose response phytotoxic impacts exhibited by the boneseed litter-mediated soil to native X. bracteatum in a more naturalistic greenhouse experiment might ensure the potential allelopathy of other chemical compounds in the boneseed invasion. The reduction of leaf relative water content and chlorophyll level in X. bracteatum suggest possible mechanisms underpinning plant growth inhibition caused by boneseed litter allelopathy. The presence of a substantial quantity of free proline in the target species also suggests that the plant was in a stressed condition due to litter allelopathy. These findings are important for better understanding the invasive potential of boneseed and in devising control strategies.

Avaliação de extratos das espécies Helianthus annuus, Brachiariabrizanthae Sorghum bicolor com potencial alelopático para uso como herbicida natural / Evaluation of extracts from Helianthus annuus, brizantha and Sorghum bicolor with allelopathic potential for use as a natural herbicide

RESUMO Objetivou-se avaliar o potencial alelopático de extratos aquosos de braquiária, girassol e sorgo na germinabilidade e crescimento inicial de alface (Lactuca sativa L.) visando o uso destes extratos como herbicida natural. O estudo foi realizado no Laboratório de Fisiologia Vegetal da Universidade Federal do Recôncavo da Bahia. Foi instalado um experimento no delineamento inteiramente casualizado, com 4 tratamentos e 6 repetições. Os tratamentos foram extratos de braquiária, girassol, sorgo e como controle, água destilada. Os extratos foram obtidos, utilizando 200 g de material vegetal para 1000 mL de água destilada. Os aquênios de alface foram distribuídos em caixa gerbox contendo duas folhas de papel germitest umedecidas com os tratamentos e levadas para câmara de germinação. A germinação foi acompanhada diariamente. Foram avaliados o tempo médio de germinação e, após dez dias, o crescimento inicial, medindo-se o comprimento da parte aérea (CPA) e o comprimento do sistema radicular (CSR). Os dados gerados foram submetidos à análise de variância e as médias comparadas pelo teste de Tukey. Com base nos resultados, os extratos de braquiária, girassol e sorgo não afetaram a germinação da alface, mas os de braquiária e sorgo aumentaram o tempo médio de germinação. Os extratos causaram aumento na parte aérea, diminuíram o crescimento do sistema radicular e a formação de plântulas normais. Por causarem inibição no crescimento do sistema radicular da alface, apresentam potencial para serem utilizados como herbicidas naturais.

ABSTRACT This study aimed to evaluate the allelopathic potential of aqueous extracts of Brachiaria, sunflower, sorghum germination and early growth of lettuce (Lactuca sativa L.), in the attempt of employing these extracts as a natural herbicide. The study was conducted at the Laboratory of Plant Physiology of the Universidade Federal do Recôncavo da Bahia. A trial was arranged in a completely randomized design with 4 treatments and 6 replications. The treatments were extracts of Brachiaria, sunflower, sorghum, and, as a control, distilled water. The extracts were obtained by using 200 g of plant material in 1000 mL of distilled water. First, the lettuce seeds were distributed in a seedling box containing two sheets of germitest moistened paper with treatments, and then were taken to a germination chamber. The germination was daily monitored. The average germination time and the initial growth were evaluated after ten days, through the measuring of the aerial part length (APL) and the root system length (RSL). The data generated were subjected to analysis of variance and the means were compared by the Tukey test. Based on the results, the extracts of Brachiaria, sunflower and sorghum did not affect the germination of lettuce, but, on the other hand, the Brachiaria and sorghum increased the germination time. The extracts caused an increase in the aerial part and reduced the root system growth and the formation of normal seedlings. Since they caused inhibition on the growth of the lettuce root system, have also potential to be used as natural herbicides.

Seasonality effect on the allelopathy of cerrado species / Efeito da sazonalidade sobre a alelopatia de espécies de cerrado

The Brazilian cerrado presents strong climate seasonality. During the dry season, plants may be exposed to stressful situations, such as a soil surface water deficit, that stimulate their chemical defenses. However, the seasonality effect on the production of allelopathic compounds of cerrado plant species is poorly understood. In this study, the phytotoxic activities of common native cerrado plants were evaluated during rainy and dry seasons. Crude leaves extracts (10% concentration: weight/volume, with dry leaves and distilled water) from eleven species were tested on lettuce and sesame germination. The negative effects on germination percentages, rates and informational entropies of the target species were higher when submitted to plant extracts from the dry season, where the germination rate was the most sensible parameter. The higher sensibility of lettuce and the germination rate parameter showed this difference. Only two exceptions had higher effects for rainy season extracts; one species showed higher negative effects on germination informational entropy of lettuce and another species on the germination rate of sesame. Thus, increases in the allelopathic activity were seen in the majority of the studied cerrado plant species during the dry season. These distinct responses to stressful situations in a complex environment such as the Brazilian cerrado may support the establishment and survival of some species.

O cerrado brasileiro apresenta forte sazonalidade climática. Durante a estação seca as plantas podem estar expostas a situações estressantes, tais como um déficit de umidade nas camadas superficiais do solo, que estimulam suas defesas químicas. No entanto, o efeito da sazonalidade na produção de compostos alelopáticos de espécies vegetais de cerrado é pouco conhecido. Neste estudo, as atividades fitotóxicas de plantas nativas comuns de cerrado foram avaliadas durante as estações chuvosa e seca. Extratos brutos de folhas (concentração 10%: peso/volume, com folhas secas e água destilada) de onze espécies foram testados sobre a germinação de alface e gergelim. Os efeitos negativos sobre as porcentagens de germinação, velocidades e entropias informacionais das espécies-alvo foram maiores quando submetidas a extratos vegetais da estação seca. A maior sensibilidade da alface e do parâmetro velocidade de germinação mostraram essa diferença. Apenas duas exceções tiveram maiores efeitos para extratos da estação chuvosa; uma espécie mostrou maiores efeitos negativos sobre a entropia informacional de germinação de alface e outra espécie sobre a velocidade de germinação de gergelim. Assim, aumentos na atividade alelopática foram vistos na maioria das espécies vegetais do cerrado estudadas durante a estação seca. Estas respostas distintas a situações estressantes em um ambiente complexo como o cerrado brasileiro podem auxiliar no estabelecimento e na sobrevivência de algumas espécies.

Seasonality effect on the allelopathy of cerrado species.

The Brazilian cerrado presents strong climate seasonality. During the dry season, plants may be exposed to stressful situations, such as a soil surface water deficit, that stimulate their chemical defenses. However, the seasonality effect on the production of allelopathic compounds of cerrado plant species is poorly understood. In this study, the phytotoxic activities of common native cerrado plants were evaluated during rainy and dry seasons. Crude leaves extracts (10% concentration: weight/volume, with dry leaves and distilled water) from eleven species were tested on lettuce and sesame germination. The negative effects on germination percentages, rates and informational entropies of the target species were higher when submitted to plant extracts from the dry season, where the germination rate was the most sensible parameter. The higher sensibility of lettuce and the germination rate parameter showed this difference. Only two exceptions had higher effects for rainy season extracts; one species showed higher negative effects on germination informational entropy of lettuce and another species on the germination rate of sesame. Thus, increases in the allelopathic activity were seen in the majority of the studied cerrado plant species during the dry season. These distinct responses to stressful situations in a complex environment such as the Brazilian cerrado may support the establishment and survival of some species.

[Allelopathic effect of Nelumbo nucifera stem and leaf tissue extract on the growth of Microcystis aeruginosa and Scenedesmus quadricanda].

Effects of Nelumbo nucifera stem and leaf tissue extract on the growth of Microcystis aeruginosa and Scenedesmus quadricanda were studied to verify its potential in entriphication control. Five concentrations of Nelumbo nucifera stem and leaf tissue extract were chosen to compare their inhibitory effects on the growth of Microcystis aeruginosa and Scenedesmus quadricanda. The result showed that the leaf extract inhibited the algae bloom more effectively than the stem extract on the whole. When the leaf extract normality was 25 g x L(-1), the highest inhibition rate of Microcystis aeruginosa and Scenedesmus quadricanda was 71.33% and 78.14%, respectively, while for the stem extract, the values were 49.78% and 52.14%. Propanamide was found in both the stem and leaf tissue extracts of Nelumbo nucifera by GC-MS analysis, with concentrations of 1.1 mg x L(-1) and 0.2 mg x L(-1), respectively. The EC50 values of the two kinds of algae were calculated by the probability method.

The impact of microbial biotransformation of catechin in enhancing the allelopathic effects of Rhododendron formosanum.

Rhododendron formosanum is distributed widely in the central mountains in Taiwan and the major allelopathic compound in the leaves has been identified as (-)-catechin, which is also a major allelochemical of an invasive spotted knapweed in North America. Soil microorganisms play key roles in ecosystems and influence various important processes, including allelopathy. However, no microorganism has been identified as an allelochemical mediator. This study focused on the role of microorganisms in the allelopathic effects of R. formosanum. The microorganism population in the rhizosphere of R. formosanum was investigated and genetic analysis revealed that the predominant genera of microorganisms in the rhizosphere of R. formosanum were Pseudomonas, Herbaspirillum, and Burkholderia. The dominant genera Pseudomonas utilized (-)-catechin as the carbon source and catalyzed the conversion of (-)-catechin into protocatechuic acid in vitro. The concentrations of allelochemicals in the soil were quantified by liquid chromatography-electrospray ionization/tandem mass spectrometry. The concentration of (-)-catechin in the soil increased significantly during the extreme rainfall in the summer season and suppressed total bacterial populations. Protocatechuic acid accumulation was observed while total bacterial populations increased abundantly in both laboratory and field studies. Allelopathic interactions were tested by evaluating the effects of different allelochemicals on the seed germination, radicle growth, and photosynthesis system II of lettuce. Protocatechuic acid exhibited higher phytotoxicity than (-)-catechin did and the effect of (-)-catechin on the inhibition of seed germination was enhanced by combining it with protocatechuic acid at a low concentration. This study revealed the significance of the allelopathic interactions between R. formosanum and microorganisms in the rhizosphere. These findings demonstrate that knowledge regarding the precise biotransformation process of (-)-catechin by microorganisms in the environment is necessary to increase our understanding of allelopathy.